block/rnbd: Use strscpy instead of strlcpy

During checkpatch analyzing the following warning message was found:
  WARNING:STRLCPY: Prefer strscpy over strlcpy - see:
  https://lore.kernel.org/r/CAHk-=wgfRnXz0W3D37d01q3JFkr_i_uTL=V6A6G1oUZcprmknw@mail.gmail.com/
Fix it by using strscpy calls instead of strlcpy.

Signed-off-by: Dima Stepanov <dmitrii.stepanov@cloud.ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Link: https://lore.kernel.org/r/20210419073722.15351-20-gi-oh.kim@ionos.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>